Re: gas mileage
What was the engine code?
Winter fuel has more detergents, not more ethanol like some believe. Ethanol rarely goes above 5% total volume even in winter. Petrol companies know most vehicles on the road yet cannot handle more than 5% ethanol without having drive-ability problems in the long term. I worked for a large firm for 7 years and most fuel deliveries that went out, were in the 3-4.5% ethanol range. Cheaper gas generally means higher detergents, and not the kind that is necessarily good for the vehicle.
Don't forget to factor in winter idle, warm up times. Drive thru's can account greatly for fuel use, especially vehicles that have a V engine and are of moderate displacement.
If you 'fixed' this engine code, don't forget to disconnect the battery for about half an hour so the PCM can relearn after the engine light has been reset, or has gone out. A lot of times, an engine code will remain stored for up to 50 restarts. It shouldn't affect mileage, but not resetting the vehicle by disconnecting the battery (negative terminal) can cause some misc problems for a short while, such as low mileage.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!